In this aerial photograph about 10 miles upriver from New Orleans, the Shell Norco Manufaturing Complex, an oil refinery, is seen in St. Charles Parish, La., Sunday, Jan. 10, 2016. The Mississippi River is above left, and the Bonnet Carre Spillway, which is used to divert river water to Lake Pontchartrain, is above right. (AP Photo/Gerald Herbert) ORG XMIT: LAGH101

In this aerial photograph about 10 miles upriver from New Orleans, the Shell Norco Manufaturing Complex, an oil refinery, is seen in St. Charles Parish, La., Sunday, Jan. 10, 2016. The Mississippi River is above left, and the Bonnet Carre Spillway, which is used to divert river water to Lake Pontchartrain, is above right. (AP Photo/Gerald Herbert) ORG XMIT: LAGH101

When Iris Carter heard that the Shell Chemical plant near her childhood home in Norco had been ordered to spend $10 million on pollution control equipment to resolve decades of allegations that the plant was violating the federal Clean Air Act, she felt a variety of emotions.

She was frustrated, she said, and angry. But she wasn’t surprised. As Carter sees it, this should have happened more than 20 years ago, when she and her family first helped start a campaign to abandon an area she said had become too polluted to live in.

"The stink in the air was so strong it knocked you back," Carter, now 66, remembers. "It was terrible."

Federal regulators this month accused Shell in a lawsuit of violating pollution laws since 1997, alleging that the energy giant failed to properly control industrial flares at the facility.

The company allowed chemicals capable of causing cancer and other ailments to permeate the air around the plant, according to the suit filed by the U.S. Environmental Protection Agency and the Department of Justice.

Then, a week ago, a settlement reached in federal court resolved those allegations through a consent decree. It commits Shell to putting in new controls designed to eliminate more than 150 tons of pollutants that had been released into the air every year.

But Norco has been the site of tension over the issue for decades, as chemical plant and oil refinery representatives, residents and environmentalists debated the extent of the pollution coming from the plant and the health ramifications various chemicals could have on the local community.

Ray Fisher, a Shell spokesman, said the agreement is "consistent" with the company's "objectives and ongoing activities to reduce emissions at the site and upgrade our flaring infrastructure."

"Shell Norco has a record of continuous improvement in environmental performance achieved through significant investment in emission reduction projects and heightened employee attention on preventing operational incidents," Fisher said. "Shell shares the goal of improving air quality, and our top priority is to protect the health and safety of community residents, our workers and the environment."

As news of the settlement spread, neighbors had mixed reactions. Many have been Norco residents for years, living through at least one major explosion at the plant and all too aware that the plant at times emitted some bad-smelling fumes.

At the same time, many residents also depend on the plant for their livelihoods.

Sal Digirolamo, the president of the Norco Civic Association, said he trusted the state and federal regulators to oversee Shell, as well as the company that gives many locals their paycheck.

As proof of Norco’s safety, he pointed to himself: At 88, he has lived in the area all his life, worked at Shell for 40 years and has never experienced health problems, he said.

“I wouldn’t move out of Norco for nothing in the world,” said Digirolamo. “How can I ever support the idea that the fumes are bad? You can’t. You gotta prove it to me.”

Federal and state government officials, too, touted their work and the consent decree, a compromise they said proved agencies could work together to keep residents safe.

"Today’s agreement demonstrates EPA’s dedication to working with states to pursue violations of laws that are critical to protecting public health and bring companies into compliance," EPA Administrator Scott Pruitt said in a news release announcing the consent decree.

But critics of the agency and of Shell sided with local environmentalists, who have been protesting the company for decades. They say it hasn’t done nearly enough to protect residents, many of whom have complained of health problems ranging from respiratory issues to cancer.

"The regulatory system was and is utterly broken," said Anne Rolfes, the founding director of the Louisiana Bucket Brigade, an environmental group.

Rolfes pointed to the small civil penalties in the consent decree, which ordered Shell to pay $350,000. Of that, $87,500 will go to the Louisiana Department of Environmental Quality.

The final amount was far less than the maximum federal law allowed: $302 million in federal civil penalties and $251 million for the state.

"That’s less than the healthcare bill for some families," Rolfes said of the penalties. "It’s completely pathetic, and that alone shows how toothless this consent decree is."

Carter agreed. She said that for decades she and others lived in fear of chemical exposure or worse from the plant and an adjoining oil refinery.

One of her sisters has cancer, another died of the autoimmune disease scleroderma, and she has been diagnosed with environment-caused asthma, she said.

"We were suffocating," Carter said. "It was agony."

Norco, short for New Orleans Refining Co., was established in 1916 when a 366-acre sugar cane field was turned into a marine petroleum supply terminal.

Norco began refining oil in 1920 and was bought by the Shell Petroleum Corp., a forerunner of Shell Oil Co., in 1929. The chemical plant, the part of Shell's operations named in the lawsuit and consent decree, was added in 1955.

In 1998, a merger with Texaco and Saudi Aramco made the refining and chemical businesses officially separate, as the oil company became part of Motiva Enterprises. Shell then assumed full ownership of Norco again last year.

Carter traces tensions over the plant to 1973, the first time there was a big explosion near it. Sparked by a 16-year-old starting a lawnmower above a leaking underground pipeline, the blast killed two people and left the community shaken.

Afterward, a group of residents formed the Concerned Citizens of Norco, which began to document chemical emissions data in the area and bring attention to abnormalities — like frequent chemical flares — happening at Shell.

“That’s what really started it all,” Carter said. “That really stirred people up. It was horrible.”

More than a decade later, there was another explosion.

Margie Richard, 76, another former member of the Norco citizens group, said she'll never forget the day seven Shell workers were killed, homes were destroyed and 159 million pounds of chemical waste were released by an explosion at the refinery one morning in 1988.

The disaster sparked more action. By 2002, with the help of the environmental group the Louisiana Bucket Brigade, residents eventually pressed Shell into relocating several residents of the Diamond neighborhood, a largely African-American section of Norco.

Shell has bought out hundreds of properties over the past 15 years.

In addition to the buyout program, the company also agreed to reduce its toxic emissions by 30 percent and to contribute $5 million to a community development fund.

Since then, though, local workers and community members have continued to complain, as environmentalists pointed out risks associated with the company's emissions of volatile organic compounds and the chemical benzene.

In recent years, Shell has been named in multiple lawsuits, including one filed in 2015 by contract welder Raymond Gaubert.

In his complaint, Gaubert alleged that his regular exposure to benzene at Shell Chemical and other facilities led to his diagnosis of multiple myeloma in 2014. He worked for Shell and other companies from 1968 through 1985.

“The health hazards of benzene have been recognized for over one hundred years,” the lawsuit said, adding that the chemical's risk has been "widely known" since 1948. “Benzene has been recognized as a carcinogen."

In the past three years, EPA data show 12 instances of "noncompliance" with federal regulations at Shell.

But members of the Louisiana Bucket Brigade and the Louisiana Environmental Action Network say the number likely was higher, as both frequently reported flaring to the EPA over the past decade.

Looking to the future, St. Charles Parish Councilman Paul Hogan said he was "somewhat concerned" about the new consent decree, particularly because the civil penalty was on the "low side."

It "probably will not act as a big deterrent to others who may be polluting our air," he said.